Misfire Troubleshooting Assist

I am Jacks N54

Specialist
Sep 10, 2018
81
1
52
0
Ventura, CA
Ride
e90 335i
Misfires on cylinder 5 have popped up on my 07 e90.

FBO, minus inlets and exhaust​
Stage 1 Walbro 450 pump​
MHD stage 2+ and e50 for the past 3-4 months​

As soon as the misfires started, I replaced #5 NGK-97506 and upgraded all coils to new Eldors. While I was in there, I noticed an abnormal amount of oil that I traced back to the Crankcase Vent Hose. Pulled it off and found my o-ring was pinched, which was leaking oil right above cylinder 5 and 6. Replaced the o-ring, cleaned the leak areas, got everything back together and cleared the 29D1 code.

Unfortunately, the misfires are still there. I just swapped #5 and #6 coil and plugs, and can tell the misfire is still there, it just hasn't gone active yet. Here's a video of the rough idle.

Searching has led me to injectors. Given that mine are original Index 1's :grimacing: it seems likely, but I don't want to jump the gun like I tend to do with diagnosis given the cost involved.

Cruise Around the Block Log (after clearing codes):


Any help with diagnosis is greatly appreciated šŸ»
 
Last edited:

I am Jacks N54

Specialist
Sep 10, 2018
81
1
52
0
Ventura, CA
Ride
e90 335i
Be sure to renew the teflon seal and decoupler on other injector, if you are just going to replace the faulty one.

I replaced the seal and the decoupler on the replacement injector, but do I need to replace both on the injector I swapped from #5 to #6? I did get the PR injector tool, so the seals were compressed before installing.
 

BloodyZ4

Private
Mar 17, 2021
29
14
0
Germany
Ride
Z4 35i DCT
Well BMW recommends replacing them, as they are one use only.
Personally I wouldn't risk it. If the decoupler isn't perfect the injector starts to oscilate in the head and will oval it out.
Since your doing the labour yourself I would just do them for peace of mind, it's only a couple of bucks, why risk it?
 
  • Agree
Reactions: Torgus